Free machining alloy tool steel



Patented July 30, 1935 2,009,715 PATENT OFFICE .FREE MACHINlNG ALLOY TOOL STEEL I hank R. Palmer, Reading, Pa., assignor to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey No Drawing. Original application January 14,

19 32, Serial N0. 586,697. Divided'and this application May 31, 1934, Serial N0. 723,305

11 Claims.

This invention relates generally to ferrous products adapted for use in the manufacture of machined articles having relatively free machining quality imparted thereto by a selenium-tellurium content, as fully set forth in my copending application Ser No. 586,697 filed Jan. 14, 1932; the present improvement forming a division of the aforesaid application, and relating particularly to the so-called tool steel class described therein.

In said application I pointed out that the ferrous alloys referred to might conveniently be divided into four general classes designated as "straight carbon steels, structural alloy steels, tool steels and special alloy steels as fully described in said application. The invention described herein applies to the third of the before mentioned groupsnamely, tool steelsf. Substantially straight carbon toolsteels have been set forth in my copending divisional application Ser. No. 714,828 filed March 9, 1934, and the present division relatesto alloy tool steels which maybe defined as ferrous alloys containing not less than .50% carbon and between 70% and 98% iron with the balance non-ferrous narily used in alloy tool steels.

My use of the term tool steel does not imply that the steel must, be used for tools only since these alloys containing more than .50% carbon are extensively used for such structural purposes as springs, ball bearings, cams, magnets, racks, gears, etc. and are very extensively used in the compov nent parts of small mechanisms such asfire-arm locks, sewing machines, adding machines, etc.

The variety of alloy tool steels is legion but 'I find it convenient to assemble them into three principal .sub-groups-namely the tungsten group the chromium group" and the "manganese group. The tungsten group contains tungsten between 1.00 and 22%--either alone. or

accompanied-by other alloying elements. A fewv of these well-known types are note'd below:

' Carbon 60 SAE 7200. Tungsten l. 50 t0 2. (X) Chromium 60 to l. 00

T TI JIZLhiIiIII k finishing iii'iiIIII: 51%,

High speed steel 2% 1. oo

. 5 to 21. 00 t0 4. 5

Cobalt high speed steel to 200 .5 to 13.00

. axunum Carbon 1.85 to 200 Mushet sell-hardening. Mm 2.00 to 2. 76 Tungsten 8. 75 to 9. 25

elements ordi- -C boa -Percent I at SAE 5195 {Chromiuin.-.-. no u- 1.

Carbon 7 1L Chromium 1.201 1.

SAE 6160 so to 1 Carbon t SAE 3270 Chromium .wto 1. Nickel 1.50 to. 2.

Carbon SAE 4150 Chromium will 1. Molybdenum- 15to Chrome magnet 8%?n i um. 3. 50 to High carbon, high chrome tool Carbon 2. .steel Chromiurn 11.00to 15.

or without other elements such 'hs vanadium, chromium, tungsten, molybdenum, etc. Another well lmownfexample is silicon-manganese steel (SAE 9250.:containing manganese .60% to .90%

and silicon 1.80% to-'2.20%. The Mushet selfhardening steel previously described contains up to 2.75% manganese, and the old "smokeless barrel steel contains about 1.25% manganese.

as 88 see sea afs'e as as A variety of other chromium tool steels are The three sub-groups set forth do not necessarlly comprehend all of the compositions that fallwithin my present tool steel: group, and they have been so classified not'to limit the scope of my invention ,but to clarify my presentation. For example, my invention provides-greatly improved machinability' in cast iron containing about 3.50% carbon. Such a product would never ordinarily be called an alloy tool steel, yet since it'ialls within the analysis limit of my arbitrary alloy tool steel? group I include it within the scope of this division.

All-ofthese tool steel compositions can be annealed (usually softer than 250 Brinell hardness) to render them commercially machinable. However, it is very desirable that the machinability be improved if possible and without too much detriment to the ultimate use of the alloys. Sulphur which has heretofore been largely used as a free machining element is abhorrent in tool steels because of the large quantity of nonmetall-ic inclusions that result from its use. I have discovered that selenium and/or tellurium can be used in percentages ranging from .03% to 2.00% to improve the machinability of alloy tool steels with a minimum of non-metallic inclusions, without interfering with the ability of these steels to harden and, in many cases, without substantial detriment to their use as finished tools and structural parts. My disparagement of sulphur in tool steels pertains of course to the ultimate utility of the finished article as I freely recognize that, from a purely machining standpoint, sulphur fulfills its normal free-machining function, and abnormally high sulphur in tool steel compositions could even be supplemented by selenium and/or tellurium with added machining advantage.

I find that the machinability of alloy tool steels shows slight but noticeable improvement with percentages of selenium and/ or tellurium as low as 05% and that the machinability increases progressively as the content of these metalloids is increased up to about 25%. Further additions up to 2% give further progressive improvement but at a slower rate so that I contemplate practically all free machining alloy tool steels can be satisfactorily made with between .5% and 25% selenium and/or tellurium. However it is to be understood that percentages between .25% and 2.00% achieve the purposes of my invention and are objectionable only because of the cost of the larger addition-the higher percentage of loss in making these large additions-and the general deterioration in the clean-.- ness of the alloy by increasing the amount of nonmetallic matter.

Quite small percentages of selenium and/or tellurium can also be used to supplement small percentages of sulphur, the effect on machinability apparently being cumulative. For example many specifications limit sulphur to less' than 04% or 05% but when supplemented by as little as 03% selenium and/or tellurium, the total percentage of free-machining metalloid may be as much as .07 to .08 which is sufficient to react favorably on the machining properties of the alloy. Thus my invention is commercially usable with selenium and/or tellurium even as low as 03%.

The use of phosphorus in alloy tool steels is as unpopular as the use of sulphur because of its embrittling effect on. the finished parts. However I have demonstrated that my selenium and/or tellurium addition, when supplemented by phosphorus yields even further improved machinability and this additional improvement is available in all cases where the embrittling effect of phosphorus does not interfere with the application of the alloy.

Phosphorus has a noticeable effect at 05% which increases progressively with further additions. Excessive brittleness is produced with phosphorus as high as .50% but I contemplate that commercially, the phosphorus will seldom be used in tool stee in percentages higher than about 12%.

Examples of the application of my invention to the three sub-groups of alloy tool steels," herein before described are given below:

Free machining tungsten tool steel Carbon 66 Manganese 35 Silicon 28 Phosphorus 017 Sulphur 011 Tungsten 18.72 Chromium 3. 46 Vanadium 1. 06 Selenium 147 Free machining chromium tool steels Carbon 98 Manganese 38 Silicon 28 Phosphorus 006 Sulphur 014 Chromium 1. 49 Selenium 2'7 Carbon 59 Manganese 43 Silicon 30 Phosphorus 010 Sulphur 020 Chromium 1. 02 Nickel l. 73 Tellurium 067 Free machining manganese tool steel Carbon .50 Manganese .78 Silicon 2.02 Phosphorus .015 Sulphur .013 Selenium .217

Machining tests made on the above examples confirm all of the other extensive experiments I have made in demonstrating the free machining effect of selenium and/or tellurium permitting of faster cutting speeds with a cleaner finish on the machined articles. Iobserve in these free machining tool steels the same anti-friction and non-galling qualities that have been characteristic of the presence of selenium and tellurium throughout my experiments. It is well-known to the art that the usefulness of many tool steel" parts such as drawing dies and mandrels, cams, etc. are limited by the tendency of the tools to pick up from the materials being fabricated. Any anti-friction or non--galling qualities imparted to the tool steel by the use of my invention contribute added value in. the utility of the tools.

Because of the poisonous nature of the fumes of tellurium emitted during the addition of this element to the molten steel bath I prefer to use selenium whenever possible. The exact quantitative equivalence of selenium and tellurium is not to be understfpod as I have frequently observed that tellurium is somewhat more potent for my purpose than selenium apart from other possible differences.

In the manufacture of my improved steel I have used elemental selenium and tellurium both in powder and stick form but I find it more desirable to first make an alloy of iron containing about 50% iron and 50% of the metalloid, and use this for additions to the molten bath. The 50% iron-metalloidalloy is heavy and is better assimilated by the bath with less loss by volatiliz'ation. In the manufacture of alloy tool steels" in an electric induction furnace, the compounding of the base analysis proceeds as usual and a few minutes before pouring the heat the ferro selenium or ferro-tellurium is added and is quickly assimilated. The loss by volatilization may range from 10% for a .10% metalloid addition to correspondingly higher losses for larger additions. In the electric arc furnace, the metalloid is best added to the flowing stream during tapping and the losses will be somewhat greater than in the induction furnace. In making open hearth alloy tool steels the metalloid is best added during the tapping operation but the losses may range and higher due to the more oxidized condition of the metal. I regard tellurium as dangerous to use in the melting shop without proper protection for the workmen.

I have tested the machinability and noted the anti-friction qualities of alloy tool steels both in the cast and rolled condition and find that my invention applies equally well to castings and rolled, forged or drawn products.

In the sub-joined claims, the term balance substantially iron is used with the understanding that the ferrous balance may contain appreciable percentages of extraneous elements of such nature and proportion that they do not alter the properties of the alloy for the purpose of my invention. For example, the presence of uranium in a high speed steel would not alter the fact that it was high speed tool steelthat it was in need of improved machinability and that the addition of my selenium and/or tellurium elements provide improved machinability. Hence such uranium would. be comprehended by my statement balance substantially iron.

Since none of the tool steels to which my present invention relates are austenitic in nature, the term non-austenitic is used in the claims to more accurately define the invention.

What I claim is:

1. The combination of .03% to 2% metalloid of the group selenium-tellurium with an inherently machinable non-austenitic base; said base comprising iron 70% to 98%, and carbon 50% to 4.00% and the balance alloying elements; and the combination of said metalloid with said base imparting materially improved machinability to the resulting alloy.

2. The combination of .03% to 2% metalloid of the group selenium-tellurium and .05% to .50% phosphorus with an inherently machinable, non-austenitic base; said base comprising iron 70% to 98%, carbon .50% to 4.00% and the balance alloying elements; and the combination of said phosphorus. and metalloid with said base imparting materially improved machinability to the resulting alloy.

3. A non-austenitic alloy tool steel containing iron 70% to 98%, tungsten 1% to 22%, carbon .50% to 2.50%,metalloid of the group selenium-tellurium .03% to 2.00%, the balance being alloying elements.

4. An' alloy steel containing tungsten 10% to 20%, chromium 2% to 6%, vanadium 50% to 3%, carbon .50% to 1.00%, metalloid of the group selenium-tellurium .03% to 50%; said alloying elements totalling not more than 28%, and the balance being substantially iron.

5. An alloy steel containing tungsten 10% to 20%, chromium 2% to 6%, vanadium 50% to 3%, carbon 50% to 1.00%, metalloid of the group selenium-tellurium .03% to .50%, phosphorus .05% to .20%; said alloying elements totalling not more than 28% and the balance being substantially iron.

6. A non-austenitic alloy tool steel" containing chromium .50% to 4%, carbon 50% to 2.50%, metalloid of the group selenium-tellurium .03% to 2.00%, other alloying elements .25% to 4.00%, balance substantially iron, with iron not exceeding 98%.

7. An alloy toolsteel containing chromium .50% to 2%, carbon .80% to 1.25%, metalloid of the group selenium-tellurium .03% to .50%, balance substantially iron, with iron not exceeding 98%.

8. An alloy tool steel containing chromium 50% to 2%, carbon .80% to 1.25%, phosphorus to .20%, metalloid of the group selenumtellurium .03% to .50%, balance substantially iron, with iron not exceeding 98%.

9. A non-austenitic alloy tool steel containing manganese 50% to 3.00%, carbon 50% to 2.50%, metalloid of the group selenium-tellurium .03% to 2.00%, other alloying elements .25% to 3.00%, balance substantially iron, with iron not exceeding 98%.

10. An alloy tool steel containing manganese 1.25% to 2.00%, carbon .50% to 1.25%, metalloid of the group selenium-tellurium .03% to .50%, balance substantially iron, with iron not exceeding 98%.

11. An alloy tool steel containing manganese 1.25% to 2.00%, carbon 50% to 1.25%, phosphorus .05% to 20%, metalloid of the group selenium-tellurium .03% to .50%, balance substantially iron, with iron not exceeding 98%.

FRANK R. PALMER. 

